This invention relates broadly to a process for obtaining valuable commercial chemical products from wood and woody materials. It pertains particularly to a process for obtaining high yields of substantially pure erythronic acid, meso tartaric acid and glyoxylic acid by the sulfurous acid hydrolysis of di- and tricarboxy celluloses and mixtures thereof. Erythronic acid, meso tartaric acid and glyoxylic acid are useful organic chemicals.
Erythronic acid is a highly water soluble organic acid useful, for example, in the manufacture of polyurethane foams and as an intermediate in the processes of the synthetic organic chemical industry.
Meso tartaric acid is of significance commercially since it is useful as a substitute for the tartaric acid of commerce as a component of lacquers and textile printing inks, and also as a complexing material for metallic ions.
Glyoxylic acid has important commercial applications in pharmaceuticals, cosmetics, photographic chemicals, agricultural chemicals and electroplating mixtures.
As will be described more fully hereinafter, it is possible to manufacture these three acids from wood and woody materials by (1) converting the wood or woody material to cellulose, e.g. paper pulp, (2) oxidizing the cellulose to dialdehyde cellulose, (3) oxidizing the dialdehyde cellulose to di- and tricarboxy celluloses, and (4) hydrolyzing the di- and tricarboxy celluloses to erythronic, meso tartaric and glyoxylic acids.
Although it heretofore in theory has been possible to carry out the above synthetic sequence, in practice a major barrier has been the difficulty of carrying out the hydrolytic reactions whereby the di- and tricarboxy celluloses are hydrolyzed to the acids in question. The di- and tricarboxy celluloses, like many cellulose derivatives, are sensitive to reaction with various chemical reagents and convert readily to complex mixtures which contain various degradation products of cellulose. Such products include tarry materials, colored products, and degradation products of low molecular weight.
It accordingly is the general object of the present invention to provide a process for the conversion of di- and tricarboxy celluloses to substantially pure erythronic, meso tartaric and glyoxylic acids in high yields, i.e. in yields of the order of 97% of the theoretical, at relatively low cost, and on a large commercial scale.
We now have discovered, and it is the essence of the present invention, that when sulfurous acid is included in the hydrolytic reaction mixture used for hydrolyzing di- and tricarboxy celluloses to erythronic, meso tartaric and glyoxylic acids, it acts as a unique catalyst in accomplishing the substantially complete conversion of the carboxy cellulose feedstock to derivative acid products in pure form, and in a form in which they may be isolated readily from the reaction mixture and separated from each other.
Broadly stated therefore, the process of the present invention comprises first forming a suspension in aqueous sulfurous acid of a carboxy cellulose-containing feedstock of the class consisting of dicarboxy cellulose, tricarboxy cellulose and mixtures thereof and thereafter treating the carboxy cellulose feedstock with the aqueous sulfurous acid at a temperature and for a time predetermined to hydrolyze the dicarboxy cellulose content of the feedstock to erythronic acid and glyoxylic acid and the tricarboxy cellulose content thereof to meso tartaric acid and glyoxylic acid.
This beneficial behavior of sulfurous acid is in marked contrast to the behavior of other acidic materials when it is attempted to use them as catalysts for the hydrolytic conversion of di- and tricarboxy celluloses to the indicated acid products. For example, when it is attempted to use sulfuric acid, hydrochloric acid, phosphoric acid and the like a certain proportion of the carboxy acid feedstock is converted to the desired organic acid products. However, the yields are low, the product is dark in color, and there are present tarry and syrupy materials which make impossible isolation of the desired organic acid products in a pure condition.